Scroll-type compressor

ABSTRACT

An orbiting scroll  6  is provided with a second communication passage  64  feeding refrigerant gas in a compression chamber  15  toward a back pressure chamber  16.  One of or each of an outer circumferential surface of a bush  4  and an inner circumferential surface of a bearing  5  is provided with a first communication passage  41  communicating an upstream side space  16   a  and a downstream side space  16   b.  The first communication passage  41  is formed so as to avoid an area at which the bush  4  receives a largest load from the plain bearing  5.  A part of the refrigerant gas compressed in the compression chamber  15  flows into the downstream side space  16   b  via the second communication passage  64,  the upstream side space  16   a  and the first communication passage  41.

TECHNICAL FIELD

The technique taught in the present specification relates to a scroll-type compressor comprising an orbiting scroll and a fixed scroll.

DESCRIPTION OF RELATED ART

A scroll-type compressor of the prior art is disclosed in Patent Document 1 (Japanese Patent Application Publication No. 2011-64189). The scroll-type compressor of Patent Document 1 is provided with an orbiting scroll, a fixed scroll disposed to face the orbiting scroll, and a shaft supporting member disposed to face the orbiting scroll at an opposite side of the fixed scroll with respect to the orbiting scroll. A compression chamber is formed between the orbiting scroll and the fixed scroll, and a back pressure chamber is formed between the orbiting scroll and the shaft supporting member. This scroll-type compressor is further provided with a rotation shaft, and an eccentric shaft offset from a rotation center of the rotation shaft. The orbiting scroll is mounted to the eccentric shaft via a bush and a bearing. A ball bearing is used as the bearing. Further, a supply passage for feeding refrigerant gas in the compression chamber toward the back pressure chamber is formed in the orbiting scroll.

In this type of scroll-type compressor, the eccentric shaft orbits by the rotation of the rotation shaft, and the orbiting scroll orbits by the orbiting of the eccentric shaft. Further, the refrigerant gas in the compression chamber is compressed by the orbiting of the orbiting scroll, and the compressed refrigerant gas is discharged to the exterior. Further, a part of the compressed refrigerant gas flows into the back pressure chamber through the supply passage of the orbiting scroll. Upon such an occasion, this refrigerant gas passes through a gap between the bearing and the bush. Pressure in the back pressure chamber is increased by the flow of refrigerant gas into the back pressure chamber, and the orbiting scroll is pressed toward the fixed scroll by this pressure. By pressing the orbiting scroll toward the fixed scroll in this manner, the orbiting scroll and the fixed scroll are prevented from separating from each other when the refrigerant gas is compressed.

In the scroll-type compressor described above, a ball bearing is used as the bearing. However, a plain bearing may be used instead of the ball bearing in order to reduce manufacturing cost. When a plain bearing is used as the bearing, the gap through which the refrigerant gas passes is narrower than when a ball bearing is used, and it becomes difficult for the refrigerant gas to flow at the portion where the bearing and the bush are in contact. Thus, it becomes difficult for the refrigerant gas compressed in the compression chamber to flow into the back pressure chamber, and the pressure in the entire back pressure chamber could not be increased rapidly. In particular, the pressure in the back pressure chamber not increasing immediately when the scroll-type compressor was started had become a problem. As a result, a state occurred in which the pressure in the back pressure chamber for pressing the orbiting scroll toward the fixed scroll becomes weak, and the orbiting scroll is not pressed sufficiently. Thus, the orbiting scroll repeatedly makes contact with and separates from the fixed scroll, and a knocking sound is generated when the orbiting scroll makes contact with the fixed scroll.

BRIEF SUMMARY OF INVENTION

The present specification aims to provide a scroll-type compressor in which manufacturing cost is suppressed, and which can be operated with reduced noise.

A scroll-type compressor disclosed herein comprises: a rotation shaft; an eccentric shaft fixed to the rotation shaft, the eccentric shaft being offset from a rotation center of the rotation shaft; a cylindrical bush fitted onto the eccentric shaft; a bearing disposed rotatably relative to the bush; an orbiting scroll supported by the bush via the bearing; a fixed scroll disposed to face the orbiting scroll; and a shaft supporting member supporting the rotation shaft and being disposed to face the orbiting scroll at an opposite side of the fixed scroll. A compression chamber is formed between the orbiting scroll and the fixed scroll. A back pressure chamber is formed between the orbiting scroll and the shaft supporting member, and the orbiting scroll is pressed toward a fixed scroll by pressure of refrigerant gas in the back pressure chamber. Refrigerant gas in the compression chamber is compressed in accordance with orbiting motion of the orbiting scroll caused by rotation of the rotation shaft through revolution of the eccentric shaft. The bearing is a plain bearing. The back pressure chamber is divided into an upstream side space and a downstream side space by the bearing. The orbiting scroll comprises a second communication passage feeding the refrigerant gas in the compression chamber toward the back pressure chamber. At least one of an outer circumferential surface of the bush and an inner circumferential surface of the bearing comprises a first communication passage communicating the upstream side space and the downstream side space. A part of the refrigerant gas compressed in the compression chamber flows into the downstream side space via the second communication passage, the upstream side space and the first communication passage. The first communication passage is formed so as to avoid an area at which the bush receives a largest load from the plain bearing.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a longitudinal sectional view of a scroll-type compressor of the embodiment;

FIG. 2 shows an enlarged view of a main part II of FIG. 1;

FIG. 3 shows an enlarged view of a main part III of FIG. 2;

FIG. 4 shows a view for explaining a load acting on a bush;

FIG. 5 is a diagram schematically showing a position of a first communication passage;

FIG. 6 shows a cross-sectional view of V-V of FIG. 1;

FIG. 7 shows an enlarged view of a main part of a scroll-type compressor of another embodiment; and

FIG. 8 shows a perspective view of a bush of the other embodiment.

DETAILED DESCRIPTION OF INVENTION

Representative, non-limiting examples of the present invention will now be described in further detail with reference to the attached drawings. This detailed description is merely intended to teach a person of skill in the art further details for practicing preferred aspects of the present teachings and is not intended to limit the scope of the invention. Furthermore, each of the additional features and teachings disclosed below may be utilized separately or in conjunction with other features and teachings to provide improved scroll-type compressor, as well as methods for using and manufacturing the same.

Moreover, combinations of features and steps disclosed in the following detailed description may not be necessary to practice the invention in the broadest sense, and are instead taught merely to particularly describe representative examples of the invention. Furthermore, various features of the above-described and below-described representative examples, as well as the various independent and dependent claims, may be combined in ways that are not specifically and explicitly enumerated in order to provide additional useful embodiments of the present teachings.

All features disclosed in the description and/or the claims are intended to be disclosed separately and independently from each other for the purpose of original written disclosure, as well as for the purpose of restricting the claimed subject matter, independent of the compositions of the features in the embodiments and/or the claims. In addition, all value ranges or indications of groups of entities are intended to disclose every possible intermediate value or intermediate entity for the purpose of original written disclosure, as well as for the purpose of restricting the claimed subject matter.

Below, embodiments will be described with reference to the accompanying figures. As shown in FIG. 1 to FIG. 3, a scroll-type compressor 1 comprises a rotation shaft 2, an eccentric shaft 3 offset from a rotation center C of the rotation shaft 2, a bush 4 fitted onto the eccentric shaft 3, and a bearing 5 disposed rotatively relative to the bush 4. Further, the scroll-type compressor 1 comprises an orbiting scroll 6 supported by the bush 4 via the bearing 5, a fixed scroll 7 disposed to face the orbiting scroll 6, and a shaft supporting member 8 disposed to face the orbiting scroll 6 at an opposite side of the fixed scroll 7 with respect to the orbiting scroll 6. A ring-shaped elastic plate 83 is interposed between the fixed scroll 7 and the shaft supporting member 8. In the scroll-type compressor 1, a compression chamber 15 is formed between the orbiting scroll 6 and the fixed scroll 7, and a back pressure chamber 16 is formed between the orbiting scroll 6 and the shaft supporting member 8. The components described above are housed in a housing 10.

The housing 10 comprises a front housing 11 on a front side, and a rear housing 12 on a rear side. The front housing 11 and the rear housing 12 are formed in a bottomed cylindrical shape, are disposed to face one another, and are fixed by bolts. A suction port 111 for intaking refrigerant gas into the housing 10 is formed in the front housing 11. Further, a discharge chamber 17 for receiving the refrigerant gas from the compression chamber 15, and a discharge port 121 for discharging the refrigerant gas in the discharge chamber 17, are formed in the rear housing 12.

The rotation shaft 2 is disposed to extend in a front and rear direction within the front housing 11. The rotation shaft 2 extends through the shaft supporting member 8 that is disposed in the front housing 11. The rotation shaft 2 is rotatably supported by a main bearing 21 and a sub bearing 22. The main bearing 21 is disposed at a central part of the shaft supporting member 8, and supports one end of the rotation shaft 2. The sub bearing 22 is disposed at a central part of a front wall of the front housing 11, and supports the other end of the rotation shaft 2. A rotor 23 and a stator 24 are disposed around the rotation shaft 2. A motor 25 is configured by the rotation shaft 2, the rotor 23 and the stator 24, and the rotation shaft 2 is rotated by operation of the motor 25.

Further, a discharging passage 29 extending in the axial direction is formed within the rotation shaft 2. One end of the discharging passage 29 communicates with the back pressure chamber 16, and the other end of the discharging passage 29 communicates with the interior of the front housing 11. The refrigerant gas in the back pressure chamber 16 can be discharged along the discharging passage 29 into the front housing 11. The refrigerant gas discharged from the discharging passage 29 flows into the front housing 11 through the gap of the sub bearing 22.

The eccentric shaft 3 is formed in a substantially cylindrical shape, is fixed to the rotation shaft 2, and extends in parallel with a center B that is parallel to the rotation shaft 2. The eccentric shaft 3 is fixed at a position offset from the rotation center C of the rotation shaft 2, and revolves together with the rotation of the rotation shaft 2. A tip of the eccentric shaft 3 is inserted into the bush 4.

The bush 4 is formed in a substantially cylindrical shape, and is fitted onto the eccentric shaft 3. When the rotation shaft 2 rotates, the bush 4 revolves together with the eccentric shaft 3 around the rotation center C of the rotation shaft 2. Further, a balance weight 42 is attached to an outer circumference of the bush 4. The balance weight 42 is a substantially fan-shaped member for canceling the centrifugal force generated by the orbiting of the orbiting scroll 6, and is provided so as to protrude in an outer circumferential direction from an end portion of the rotation shaft 2 of the bush 4. The balance weight 42 is formed at an opposite side of the eccentric shaft 3 with respect to the rotation center C.

A groove-shaped (first) communication passage 41 is formed in an outer circumferential surface of the bush 4. The first communication passage 41 is formed in a concave shape by cutting into the outer circumferential surface of the bush 4. Therefore, the first communication passage 41 faces an inner circumferential surface of the bearing 5. The first communication passage 41 has an opening 411. The opening 411 faces a radially outward of the bush 4. The opening 411 faces the inner circumferential surface of the bearing 5. The first communication passage 41 extends linearly in the axial direction of the bush 4. The first communication passage 41 passes from one end to the other end in the axial direction of the bush 4. As shown in FIG. 4, a resultant force Fb of centrifugal force Fmr, compression reaction force Fθ applied in a tangential direction to the orbiting scroll 6, and compression reaction force Fr in the radial direction is applied as a load to the orbiting scroll 6. A load in an opposite direction to the resultant force Fb is applied to the eccentric shaft 3, whereupon the eccentric shaft 3 presses the bush 4, and the bush 4 presses the bearing 5. As shown in FIG. 5, when the rotation shaft 2 rotates, the eccentric shaft 3 which is at a position offset from the rotation center C presses the bush 4 in the direction of the upper left side of the drawing. In particular, in this embodiment, if a imaginary line L is set which passes through the rotation center C and an axis of the bush 4, a center of the eccentric shaft 3 is at a position displaced to the upper left direction from the imaginary line L. The first communication passage 41 is formed so as to avoid the area where the largest load is applied to the bush 4, this being an area of the bush 4 having the largest pressure pressing upon the bearing 5 when the bush 4 revolves. In particular, it is preferred that the first communication passage 41 is formed at an opposite side (a side where the axis of the eccentric shaft 3 is not present with respect to the imaginary line L (second side) from a side where the bush 4 presses the bearing 5 (a side where the axis of the eccentric shaft 3 is present with respect to the imaginary line L (first side)). Consequently, when the bush 4 revolves, the bush 4 is not in close contact with the inner circumferential surface of the bearing 5, and the first communication passage 41 is in an opened state.

Further, it is preferred that the opening 411 of the first communication passage 41 is in a position not facing the balance weight 42. In case the first communication passage 41 is in a position not facing the balance weight 42, the flow of refrigerant gas is not blocked by the balance weight 42. As shown in FIG. 5, the balance weight 42 is formed integrally on one side of the outer periphery of the bush 4. A position not facing the balance weight 42 is a position where the balance weight 42 is not formed on the outer periphery of the bush 4. That is, in FIG. 5, the balance weight 42 is not formed on the portion of the outer periphery of the bush 4 indicated by hatching. The opening of the first communication passage 41 is formed in any position in the portion indicated by the hatching in FIG. 5.

As shown in FIG. 3, the bearing 5 comprises an inner sliding member 51 facing the bush 4, and an outer sliding member 53 facing the orbiting scroll 6. The inner sliding member 51 is press-fitted to the outer sliding member 53, fixing the inner sliding member 51 and the outer sliding member 53 to one another. The inner sliding member 51 comprises an inner layer 511 in contact with a bush 33, a back metal 513 in contact with the outer sliding member 53, and an intermediate layer 512 for coupling the inner layer 511 and the back metal 513. In the bearing 5, the inner layer 511 of the inner sliding member 51 and the bush 4 slide with respect to one another, and the outer sliding member 53 and the orbiting scroll 6 slide with respect to one another. Thus, the bearing 5 and the bush 4 rotate relative to one another, and the bearing 5 and the orbiting scroll 6 rotate relative to one another.

The orbiting scroll 6 is disposed at the rear of the bush 4 and the bearing 5. The orbiting scroll 6 comprises an orbiting base portion 61 facing the bearing 5, and an orbiting spiral wall portion 62 (see FIG. 6) that protrudes from the orbiting base portion 61 toward the fixed scroll 7. A front surface of the orbiting base portion 61 makes contact with a rear surface of the elastic plate 83. Therefore, the orbiting scroll 6 can orbit while sliding relative to the elastic plate 83. When elastically deformed, the elastic plate 83 urges the orbiting scroll 6 toward the fixed scroll 7 due to restoring force. On the other hand, the fixed scroll 7 is disposed at the rear of the orbiting scroll 6. The fixed scroll 7 comprises a fixed base portion 71 facing the orbiting base portion 61, and a fixed spiral wall portion 72 (see FIG. 6) that protrudes from the fixed base portion 71 toward the orbiting scroll 6. The orbiting scroll 6 and the fixed scroll 7 are disposed in a state where each base portion 61, 71 faces one another, and each wall portion 62, 72 is engaged with each other. The orbiting scroll 6 and the fixed scroll 7 are disposed in a state where centers thereof are spaced apart, and the spiral wall portions 62, 72 are in a deviated phase with one another (see FIG. 6).

The orbiting scroll 6 comprises a cylindrically-shaped boss portion 63 that protrudes toward the bearing 5 from the orbiting base portion 61. The bearing 5 is inserted into the boss portion 63. A tip 621 of the orbiting wall portion 62 of the orbiting scroll 6 makes contact with the fixed base portion 71 of the fixed scroll 7 via lubricating oil included in the refrigerant gas. The orbiting wall portion 62 is formed so as to expand outward in a spiral-shape from a center portion of the orbiting base portion 61 (see FIG. 6). One (second) communication passage 64 that feeds the refrigerant gas in the compression chamber 15 toward the back pressure chamber 16 is formed in the orbiting wall portion 62. The second communication passage 64 penetrates the orbiting wall portion 62. When the tip 621 of the orbiting wall portion 62 is making contact with the fixed base portion 71 of the fixed scroll 7, the surrounding of the opening of the second communication passage 64 is sealed and closed by the lubricating oil. In contrast, when the orbiting scroll 6 is pressed forward and the tip 621 of the orbiting wall portion 62 is spaced apart from the fixed base portion 71 of the fixed scroll 7, the second communication passage 64 is opened. When the second communication passage 64 has been opened, the refrigerant gas in the compression chamber 15 flows into the second communication passage 64, and is fed toward the back pressure chamber 16.

The back pressure chamber 16 is divided by the bearing 5 into an upstream side space 16 a and a downstream side space 16 b. Refrigerant gas that has passed through the second communication passage 64 passes through the upstream side space 16 a, then flows through the first communication passage 41 toward the downstream side space 16 b. The second communication passage 64, the upstream side space 16 a, and the first communication passage 41 communicate.

The fixed scroll 7 is fixed to the housing 10. A discharge opening 73 for discharging the refrigerant gas is formed in the fixed scroll 7. The discharge opening 73 penetrates the fixed base portion 71 of the fixed scroll 7, and communicates with the compression chamber 15. The refrigerant gas compressed in the compression chamber 15 is discharged from the discharge opening 73 into the discharge chamber 17, then is discharged to the exterior from the discharge port 121. Further, a tip 721 of the fixed wall portion 72 of the fixed scroll 7 makes contact with the orbiting base portion 61 of the orbiting scroll 6 via the lubricating oil included in the refrigerant gas. The fixed wall portion 72 is formed so as to expand outward in a spiral-shape from a center portion of the fixed base portion 71 (see FIG. 6).

The shaft supporting member 8 comprises a body portion 81, and a fixing portion 82 that projects around the body portion 81. The body portion 81 is disposed at a center portion of the housing 10, and the fixing portion 82 is fixed to a side wall of the housing 10. The shaft supporting member 8 is shaped such that the body portion 81 projects further forward than the fixing portion 82, and a center portion thereof is recessed. The back pressure chamber 16 surrounded by the body portion 81 and the fixing portion 82 is formed between the shaft supporting member 8 and the orbiting scroll 6. Further, a refrigerant gas feeding path (not shown) for feeding the refrigerant gas within the front housing 11 to the compression chamber 15 is formed in the fixed scroll 7 and the shaft supporting member 8.

The compression chamber 15 is surrounded by the orbiting base portion 61 and the orbiting wall portion 62 of the orbiting scroll 6 and by the fixed base portion 71 and the fixed wall portion 72 of the fixed scroll 7. The compression chamber 15 forms a crescent-shaped space surrounded by the orbiting spiral wall portion 62 and the fixed wall portion 72 (see FIG. 6). In the compression chamber 15, the orbiting scroll 6 compresses the refrigerant gas inside by orbiting with respect to the fixed scroll 7. The refrigerant gas compressed in the compression chamber 15 is discharged from the discharge opening 73 formed in the fixed scroll 7. A part of the compressed refrigerant gas flows into the second communication passage 64 of the orbiting scroll 6.

The refrigerant gas that has passed through the first communication passage 41 of the bush 4 flows into the back pressure chamber 16. The refrigerant gas in the back pressure chamber 16 presses the orbiting scroll 6 toward the fixed scroll 7.

Next, the operation of the scroll-type compressor comprising the configuration described above will be described. First, when the motor 25 is operated, the rotation shaft 2 rotates, and the eccentric shaft 3 orbits by the rotation of the rotation shaft 2. Further, the orbiting scroll 6 orbits by the orbiting of the eccentric shaft 3, and the refrigerant gas in the compression chamber 15 is compressed by the orbiting of the orbiting scroll 6. The compressed refrigerant gas is discharged from the discharge opening 73 into the discharge chamber 17. Further, when the pressure of the compression chamber 15 is increased by the compression of the refrigerant gas in the compression chamber 15, the orbiting scroll 6 is pressed forward by this pressure. In this state, the second communication passage 64 of the orbiting scroll 6 is opened, and a part of the refrigerant gas in the compression chamber 15 flows into the second communication passage 64. The refrigerant gas that has flowed into the second communication passage 64 flows from the second communication passage 64 into the upstream side space 16 a. Then this refrigerant gas flows from the upstream side space 16 a into the first communication passage 41 of the bush 4, and flows through the first communication passage 41 into the downstream side space 16 b. Thus, the pressure of the entire refrigerant gas in the back pressure chamber 16 increases, and the orbiting scroll 6 is pressed toward the fixed scroll 7 by this pressure. In this manner, the orbiting scroll 6 is supported by pressing the orbiting scroll 6 toward the fixed scroll 7, and the orbiting scroll 6 and the fixed scroll 7 do not separate when the refrigerant gas is compressed.

As is clear from the above description, since the bearing 5 between the bush 4 and the orbiting scroll 6 is a plain bearing, manufacturing cost can be suppressed compared to a conventional ball bearing, and downsizing in the radial direction is possible. Further, the refrigerant gas can rapidly flow from the compression chamber 15 into the back pressure chamber 16 via the groove-shaped first communication passage 41 formed in the bush 4. Therefore, the pressure of the refrigerant gas in the back pressure chamber 16 can be rapidly increased, and the orbiting scroll 6 can rapidly be pressed toward the fixed scroll 7 when the scroll-type compressor 1 is started. Consequently, the orbiting scroll 6 can be prevented from making contact with and separating from the fixed scroll 7 by the pressure of the refrigerant gas in the back pressure chamber 16, and the knocking sound generated by the orbiting scroll 6 repeatedly making contact with and separating from the fixed scroll 7 can be prevented. Therefore, according to the scroll-type compressor 1 taught in the present specification, operation with reduced noise can be made possible while manufacturing cost is suppressed.

Further, in the configuration described above, the first communication passage 41 is formed. That is, the first communication passage 41 is formed at the opposite side to the side where the bush 4 is caused by the load to press against the bearing 5 when the bush 4 revolves. Thus, since the contact area of the bush 4 and the bearing 5 can be ensured and the load can be received at the area where the bush 4 receives the largest load when the bush 4 revolves, and the first communication passage 41 is formed at the side not fitting tightly with the bearing 5, the first communication passage 41 is easily maintained in an opened state. Therefore, the refrigerant gas easily passes through the first communication passage 41, and the refrigerant gas can rapidly be introduced into the back pressure chamber 16. Further, since the opening 411 of the first communication passage 41 is at a position not facing the balance weight 42, the flow is not blocked by the balance weight 42, and the refrigerant gas can be introduced rapidly.

One embodiment was described above, but the specific features are not restricted the above embodiment. For example, the first communication passage 41 was configured to be formed in the bush 4 in the above embodiment, but is not limited to this configuration. As shown in FIG. 7, the first communication passage 41 may alternatively or additionally be formed in the bearing 5. In this case, the first communication passage 41 is formed in a groove shape in the inner circumferential surface of the bearing 5. More specifically, the first communication passage 41 is formed in the inner sliding member 51 of the bearing 5, and faces the outer circumferential surface of the bush 4. Further, the first communication passage 41 extends linearly from one end to the other end of the inner sliding member 51. With this configuration, the refrigerant gas flows rapidly to the back pressure chamber 16 via the groove-shaped first communication passage 41.

Further, in the above embodiment, the first communication passage 41 extends in the axial direction of the bush 4. However, as shown in FIG. 8, the first communication passage 41 may alternatively or additionally extend in the circumferential direction of the bush 4, aside from the axial direction. Thus, the first communication passage 41 may be formed so as to extend in a spiral shape in the outer circumferential surface of the bush 4. Further, the first communication passage 41 need not necessarily be formed along the entire circumference of the circumferential direction of the bush 4. In the present embodiment, the first communication passage 41 is formed across half the circumference of the bush 4 in the circumferential direction. Even according to this configuration, the refrigerant gas flows rapidly into the back pressure chamber 16 via the first communication passage 41. Further, according to this configuration, the bush 4 and the bearing 5 rotate more smoothly relative to one another compared to the configuration in which the first communication passage 41 extends linearly in the axial direction of the bush 4.

Further, as in the case where the first communication passage 41 is formed in the bearing 5 alternatively or additionally to being formed in the bush 4, the first communication passage 41 may be formed so as to extend in the axial direction of the bearing 5, and as an alternative or addition thereto, in the circumferential direction of the bearing 5.

Further, in the above embodiment, the second communication passage 64 is formed in the orbiting wall portion 62 of the orbiting scroll 6. However, the second communication passage 64 is not restricted to this configuration, but may be formed in the orbiting base portion 61 of the orbiting scroll 6. Even according to this configuration, the refrigerant gas in the compression chamber 15 can be fed through the second communication passage 64 toward the back pressure chamber 16. 

What is claimed is:
 1. A scroll-type compressor comprising: a rotation shaft; an eccentric shaft fixed to the rotation shaft, the eccentric shaft being offset from a rotation center of the rotation shaft; a cylindrical bush fitted onto the eccentric shaft; a bearing disposed rotatably relative to the bush; an orbiting scroll supported by the bush via the bearing; a fixed scroll disposed to face the orbiting scroll; and a shaft supporting member supporting the rotation shaft and being disposed to face the orbiting scroll at an opposite side from the fixed scroll, wherein a compression chamber is formed between the orbiting scroll and the fixed scroll, a back pressure chamber is formed between the orbiting scroll and the shaft supporting member, the orbiting scroll is pressed toward a fixed scroll by pressure of refrigerant gas in the back pressure chamber, refrigerant gas in the compression chamber is compressed in accordance with orbiting motion of the orbiting scroll caused by rotation of the rotation shaft through revolution of the eccentric shaft, the bearing is a plain bearing, the back pressure chamber is divided into an upstream side space and a downstream side space by the bearing, at least one of an outer circumferential surface of the bush and an inner circumferential surface of the bearing comprises a first communication passage communicating the upstream side space and the downstream side space, the orbiting scroll comprises a second communication passage feeding the refrigerant gas in the compression chamber toward the back pressure chamber, a part of the refrigerant gas compressed in the compression chamber flows into the downstream side space via the second communication passage, the upstream side space and the first communication passage, and the first communication passage is formed so as to avoid an area at which the bush receives a largest load from the plain bearing.
 2. The scroll-type compressor according to claim 1, wherein a balance weight is integrally attached to the bush, and an opening of the first communication passage is located in an area not opposing the balance weight.
 3. The scroll-type compressor according to claim 1, wherein a imaginary line set to include a rotation shaft axis and a bush axis defines a first side on which an eccentric shaft axis exists and a second side on which the eccentric shaft axis does not exist, and the first communication passage is formed on the second side.
 4. The scroll-type compressor according to claim 1, wherein the first communication passage extends along one of or each of an axial direction and a circumferential direction of the bush, and an axial direction and a circumferential direction of the bearing.
 5. The scroll-type compressor according to claim 1, wherein the first communication passage is formed on the bush.
 6. The scroll-type compressor according to claim 1, wherein the first communication passage is formed on the bearing.
 7. The scroll-type compressor according to claim 1, wherein the bearing comprises an inner sliding member in contact with the bush and an outer sliding member in contact with the orbiting scroll, and the first communication passage is formed on the inner sliding member.
 8. The scroll-type compressor according to claim 1, wherein the rotation shaft comprises a discharging passage through which the refrigerant gas in the back pressure chamber is discharged. 